ORC turbine and generator, and method of making a turbine

ABSTRACT

A turbine and a turbine-generator device for use in electricity generation. The turbine has a universal design and so may be relatively easily modified for use in connection with generators having a rated power output in the range of 50 KW to 5 MW. Such modifications are achieved, in part, through use of a modular turbine cartridge built up of discrete rotor and stator plates sized for the desired application with turbine brush seals chosen to accommodate radial rotor movements from the supported generator. The cartridge may be installed and removed from the turbine relatively easily for maintenance or rebuilding. The rotor housing is designed to be relatively easily machined to dimensions that meet desired operating parameters.

RELATED APPLICATION DATA

This application is a divisional of U.S. patent application Ser. No.16/120,351, filed Sep. 3, 2018, entitled “ORC TURBINE AND GENERATOR, ANDMETHOD OF MAKING A TURBINE,” now allowed, which application is adivisional of U.S. patent application Ser. No. 15/227,604, filed Aug. 3,2016, entitled “ORC TURBINE AND GENERATOR, AND METHOD OF MAKING ATURBINE,” now U.S. Pat. No. 10,069,378, which application is adivisional application of U.S. patent application Ser. No. 14/797,639,filed Jul. 13, 2015, entitled “ORC TURBINE AND GENERATOR, AND METHOD OFMAKING A TURBINE,” now abandoned, which application is a divisionalapplication of U.S. patent application Ser. No. 13/937,978, filed Jul.9, 2013, entitled “Overhung Turbine and Generator System With TurbineCartridge,” now U.S. Pat. No. 9,083,212, which application claims thebenefit of priority of U.S. Provisional Patent Application Ser. No.61/699,649, filed Sep. 11, 2012, entitled “Axial Overhung Turbine andGenerator System For Use In An Organic Rankine Cycle.” All of theseapplications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of turbinegenerator power systems for industrial waste heat recovery and otherapplications. In particular, the present invention is directed to anoverhung turbine coupled to a direct-drive, electrical power generator.

BACKGROUND

Concerns about climate change and rising energy costs, and the desire tominimize expenses in various industrial operations, together lead to anincreased focus on capturing waste heat developed in such operations.Organic Rankine Cycle (“ORC”) turbine generator electrical power systemshave been used in industrial waste heat recovery. Unfortunately, knownsystems for capturing waste heat and converting it to electricity areoften too large for the space available in certain industrialoperations, are less efficient than desired, require more heat tooperate efficiently than is available, are too expensive to manufacturefor certain applications, or require more maintenance than is desired.In other applications, such as geothermal energy recovery and certainocean thermal energy projects, abundant heat is available and anefficient ORC system is a satisfactory means for conversion of such heatto electricity. Even in such other applications, however, known ORCsystems tend to be too expensive for some such applications, are lessefficient than desired and/or require more maintenance than is desired.

SUMMARY OF THE INVENTION

In one implementation, the present disclosure is directed to an axialturbine with interchangeable components. The axial turbine includes ahousing having an interior and a first axis of rotation; a plurality ofrotor plates, each having a centerline, a first contact surface and asecond contact surface contacting said first contact surface, said firstand second contact surfaces being substantially parallel and each ofsaid first and second contact surfaces being flat in the range 0.00005″to 0.020″, wherein said plurality of rotor plates are positionedproximate one another so that said centerlines thereof are mutuallycoaxial and are coaxial with said first axis of rotation so as to definerotor portions of a multi-stage rotor assembly, each of said pluralityof rotor plates having a radially outermost portion; a plurality ofstator plates, each having a centerline, a first contact surface and asecond contact surface contacting said first contact surface, said firstand second contact surfaces being substantially parallel and each ofsaid first and second surfaces being flat in the range 0.00005″ to0.020″, wherein said plurality of stator plates are positioned proximateone another so that said centerlines of said stator plates are mutuallycoaxial and are coaxial with said first axis of rotation so as to definestator portions of a multi-stage stator assembly, each of said pluralityof stator plates having a radially innermost portion; wherein saidplurality of rotor plates are positioned in alternating relationshipwith corresponding respective ones of said plurality of stator plates soas to define a multi-stage rotor assembly with an upstream direction,further wherein at least one of said plurality of rotor plates includesa first plurality of vanes with an axial chord and an adjacent one ofsaid plurality of stator plates includes a second plurality of vaneswith an axial chord, wherein said first plurality of vanes is axiallyspaced from said second plurality of vanes to define a space having anaxial dimension that is no more than two axial chords to ¼ of 1% of anaxial chord, as measured with respect to the axial chord of the one ofsaid rotor plate and stator plate immediately upstream of said space.

In another implementation, the present disclosure is directed to amethod of manufacturing plurality of turbines wherein each turbine insaid plurality of turbines is manufactured starting with one of aplurality of substantially identical turbine hoods, each turbine hoodhaving a cavity for receiving a rotor stage and a floor with a firstthickness, wherein the floor defines a portion of the cavity and thecavity has an inside diameter D1. The method includes machining materialaway from the floor of a first one of said plurality of turbine hoods toincrease the inside diameter D1 of the cavity to an inside diameter D2,where D2 is selected to permit the cavity to accommodate a first rotorstage having a radial height H1, the first rotor stage being designedand sized to be positionable in the cavity of the first one of theplurality of universal turbine hoods proximate the floor of the cavity;and machining material away from the floor of a second one of saidplurality of turbine hoods to increase the inside diameter D1 of thecavity to an inside diameter D3, wherein D3 is different than D2 and isselected to permit the cavity to accommodate a second rotor stage havinga radial height H2 that is different than radial height H1, the secondrotor stage designed and sized to be positionable in the cavity of thesecond one of the plurality of turbine hoods proximate the floor of thecavity.

In yet another implementation, the present disclosure is directed to asystem for generating electricity. The system includes an electricgenerator having a proximal end, a distal end, a generator rotor and astator, said generator rotor being disposed for rotational movementwithin said stator about a rotational axis, said generator alsoincluding a first magnetic radial bearing positioned adjacent saidproximal end, and a second magnetic radial bearing positioned adjacentsaid distal end, said first and second magnetic radial bearingssurrounding said generator rotor and supporting said generator rotorsuch that said generator rotor does not move, during operation, morethan a first radial distance out of coaxial alignment with said rotationaxis, said generator further including at least one brush seal extendingradially inwardly toward said generator rotor and a brush seal seatpositioned radially inwardly of said at least one brush seal a firstdistance selected so that said at least one brush seal is positionedproximate said brush seal seat, said at least one brush seal being sizedand configured, and having a rigidity selected to, support saidgenerator rotor during startup and shut down such that said generatorrotor does not deviate more than a second radial distance out ofco-axial alignment with said rotational axis, said second radialdistance being 0.8 to 5 times said first radial distance; and a turbinehaving at least one turbine stator and at least one turbine rotorsupported for rotational movement relative to said at least one turbinestator about said rotational axis, said at least one turbine rotor beingcoupled with said generator rotor so as to rotationally drive saidgenerator rotor, said turbine having a first end attached to saidproximal end of said generator, wherein said at least one turbine statorincludes a plurality of turbine stator plates, said at least one turbinerotor includes a plurality of turbine rotor plates, and said turbinestator plates and turbine rotor plates have substantially flat contactsurfaces.

In a further implementation, the present disclosure is directed to asystem for generating electricity. The system includes an electricgenerator having a proximal end, a distal end, a generator rotor and astator, said generator rotor being disposed for rotational movementwithin said stator about a rotational axis, said generator alsoincluding a first magnetic radial bearing positioned adjacent saidproximal end, and a second magnetic radial bearing positioned adjacentsaid distal end, said first and second magnetic radial bearingssurrounding said generator rotor and retaining said generator rotor,during operation, in substantially coaxial alignment with respect tosaid rotational axis; and a turbine having at least one turbine statorand at least one turbine rotor supported for rotational movementrelative to said at least one turbine stator about said rotational axis,said at least one turbine rotor being coupled with said generator rotorso as to rotationally drive said generator rotor, said turbine having afirst end attached to said proximal end of said generator, wherein saidat least one turbine stator includes a plurality of stator plates, saidat least one turbine rotor includes a plurality of turbine rotor plates,and said stator plates and turbine rotor plates have substantially flatcontact surfaces, wherein said turbine has a stage reaction that rangesfrom −0.1 to +0.3.

In a further implementation, the present disclosure is directed to asystem for generating electricity. The system includes an electricgenerator having a proximal end, a distal end, a generator rotor and astator, said generator rotor being disposed for rotational movementwithin said stator about a rotational axis, said generator alsoincluding a first fluid film bearing positioned adjacent said proximalend, and a second fluid film bearing positioned adjacent said distalend, said first and second fluid film bearings surrounding saidgenerator rotor and retaining said generator rotor, during operation, insubstantially coaxial alignment with respect to said rotational axis;and a turbine having at least one turbine stator and at least oneturbine rotor supported for rotational movement relative to said atleast one stator about said rotational axis, said at least one turbinerotor being coupled with said generator rotor so as to rotationallydrive said generator rotor, said turbine having a first end attached tosaid proximal end of said generator, wherein said at least one turbinestator includes a plurality of stator plates, said at least one turbinerotor includes a plurality of turbine rotor plates, and said statorplates and turbine rotor plates have substantially flat contactsurfaces, wherein said turbine has a stage reaction that ranges from−0.1 to +0.3.

In yet a further implementation, the present disclosure is direct to aturbine. The turbine includes at least one stator including a pluralityof stator plates having substantially flat contact surfaces; and atleast one rotor supported for rotational movement relative to said atleast one stator about said rotational axis, said at least one rotorincluding a plurality of turbine rotor plates having substantially flatcontact surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a schematic depiction of an ORC turbine-generator system;

FIG. 2 is a schematic depiction of the turbine and generator of thesystem shown in FIG. 1 , with interior details of the generator beingschematically illustrated;

FIG. 3 is similar to FIG. 1 , except that an alternative embodiment ofthe ORC turbine-generator system is depicted;

FIG. 4 a is a cross-sectional view of a multi-stage axial turbineembodiment of the turbine assembly depicted in FIG. 1 and a partiallybroken-away view of the generator depicted in FIG. 1 showing,schematically, bearings included in one embodiment of the generator,with the rotor and stator of the generator removed for clarity ofillustration;

FIG. 4 b is similar to FIG. 4 a , except that a single-stage radialturbine embodiment of the turbine assembly depicted in FIG. 1 is shown;

FIG. 4 c is similar to FIG. 4 b , except that a multi-stage radialturbine embodiment of the turbine assembly depicted in FIG. 4 b isshown;

FIG. 4 d is similar to FIG. 4 c , except that the rotors of themulti-stage radial turbine assembly depicted in FIG. 4 c are arranged inback-to-back configuration;

FIG. 5 is cross-sectional view of one embodiment of a turbine cartridgeusable in the turbine shown in FIG. 4 a;

FIG. 6 is an enlarged cross-sectional view of a portion of the turbineshown in FIG. 4 a , illustrating a portion of the hood backplate and theentire turbine cartridge;

FIG. 7 is a perspective view showing the relative placement of twostator plates and one rotor plate with its stationary spacer plate usedin a multi-stage embodiment of the turbine depicted in FIG. 4 a;

FIG. 8 is a perspective view of three rotor plates used in a multi-stageembodiment of the turbine depicted in FIG. 4 a showing the relativeplacement of the plates;

FIG. 9 is a cross-sectional side view of a portion of the turbine shownin FIG. 6 illustrating brush seals and other details of the turbine; and

FIG. 10 is similar to FIG. 9 , except that it depicts an alternativeembodiment of the turbine.

DETAILED DESCRIPTION

The present disclosure is directed to a turbine powered electricalgenerator for use in an Organic Rankine Cycle (ORC), Kalina cycle, orother similar cycles, industrial operations that generates waste heat,or in connection with other heat sources, e.g., a solar system or anocean thermal system. High-pressure hot gas from a boiler, which isheated by the heat source, enters the turbine housing and is expandedthrough the turbine to turn the rotor, which turns the generator shaftto generate electricity, as described more below.

Referring to FIG. 1 , turbine-generator assembly 20 is intended for usein an ORC system 22. For convenience of discussion, system 22 isreferred to and described as ORC system 22. It is, however, to beappreciated that other thermodynamic processes, such as a Kalina cycleprocess and bottoming cycle processes, are also encompassed by thepresent invention. Turbine-generator assembly 20 includes a turbine 24and a generator 26 connected to, and driven by, the turbine. Beforediscussing turbine-generator assembly 20 in more detail, discussion ofORC system 22 is provided.

ORC system 22 includes a boiler 28 that is connected to a heat source30, such as waste heat from an industrial process. Boiler 28 provideshigh-pressure hot vapor via connection 32 to turbine 24. As discussedmore below, the hot vapor, aka, the working fluid, is expanded inturbine 24, where its temperature drops, and is then exhausted from theturbine and delivered via fluid connection 34 to condenser 36. Incondenser 36, the vapor cooled in turbine 24 is cooled further,typically to a liquid state, and then a first volume of such liquid isdelivered via fluid connection 38 to pump 40, where the liquid isreturned via connection 42 to boiler 28. This liquid is then reheated inboiler 28 by heat from heat source 30 through a heat exchanger or otherstructure (none shown) in the boiler and then, repeating the cycle, isreturned as high-pressure hot vapor via fluid connection 32 to turbine24.

Turning now to FIGS. 1 and 2 , a second volume of the cooled liquidexiting condenser 36 is, in one embodiment, delivered by pump 50 viafluid connection 52 to vaporizer 54 and from the vaporizer to generator26 via fluid connection 58. Fluid from pump 50 is also delivered viafluid connection 56 to generator 26, in particular cooling jacket 76,discussed more below. In other embodiments, it may be desirable to omitpump 50 and instead deliver liquid that is output from pump 40 via fluidconnection 57 to fluid connections 52 and 56. Vaporizer 54 vaporizes atleast some of the second volume of liquid from condenser 36 and deliversthe cooling vapor via fluid connection 58 to generator 26. Asillustrated in FIG. 2 , generator 26 includes a fluid gap 70, a stator72 and a generator rotor 74, with the fluid gap (e.g., gas or atomizedliquid) being positioned between the stator and rotor. Generator rotor74 rotates relative to stator 72 about rotational axis 106.

The cooling vapor is introduced into gap 70, and as the vapor passesthrough gap 70 it extracts heat from stator 72 and generator rotor 74,which vapor is then exhausted via fluid connection 34, along with thehot vapor exhausted from turbine 24, for cooling by condenser 36.Optionally, as illustrated in FIGS. 1 and 3 , vapor exhausted fromgenerator 26 may be delivered via fluid connection 37 directly tocondenser 36 rather than being combined with vapor exhausted fromturbine 24. Turbine 24 has a through flow rate and, in one embodiment,the second volume of the vapor (working fluid) introduced into gap 70travels through the gap with a flow rate that is no more than 50% of thethrough flow rate. Typically, although not necessarily, generator 26 ishermetically sealed to ensure working fluid present in gap 70 does notescape except via fluid connection 34, or fluid connection 37, ifprovided.

Referring now to FIGS. 1-4 , in one embodiment generator 26 issurrounded by a cooling jacket 76 (FIGS. 2 and 4 ) for cooling thegenerator. Cooling liquid pumped by pump 50 to generator 26 via fluidconnection 56 is delivered to cooling jacket 76 via inlets 77 (FIG. 4 ).As the cooling liquid circulates through cooling jacket 76, it extractsheat from stator 72 and other components of generator 26. Aftercompleting its passage through cooling jacket 76, the cooling liquid,now somewhat hotter, is removed from generator 26 via fluid connection78, after exiting fluid outlet 79 in the cooling jacket, and returned tocondenser 36.

Turning next to FIGS. 2 and 3 , in another embodiment of ORC system 22,atomized cooling liquid, rather than vaporized liquid, is provided togap 70 in generator 26. Except as specifically discussed below, theembodiment of ORC system 22 illustrated in FIG. 3 is essentiallyidentical to the embodiment of the system shown in FIG. 1 , and sodescription of identical elements is not provided in the interest ofbrevity. Unlike the embodiment of ORC system 22 illustrated in FIG. 1 ,no vaporizer is provided in the embodiment illustrated in FIG. 3 .Instead a portion of the cooling liquid delivered via fluid connection56 to generator 26 is provided by fluid connection 80 to atomizer 82positioned proximate to the generator. Atomizer 82 atomizes the coolingliquid, which is then delivered to gap 70 in generator 26, where therelatively cool atomized liquid extracts heat from stator 72 andgenerator rotor 74 as it travels through the gap, including through thelatent heat of vaporization with respect to portions of the atomizedliquid that are vaporized by the heat in the stator and rotor. Theatomized liquid is then extracted from generator 26 via fluid connection34 along with the working fluid exhausted from turbine 24. In FIGS. 2and 3 , atomizer 82 is depicted in dotted view to indicate that it is anoptional element used in connection with one embodiment of theinvention. As discussed above, in one embodiment, the second volume ofthe atomized liquid (working fluid) introduced into gap 70 travelsthrough the gap with a flow rate that is no more than 50% of the throughflow rate of turbine 24.

In some applications, it may be desirable to provide just cooling ofstator 72 via cooling jacket 76, and not provide vapor or atomizedliquid to gap 70. In other applications, the reverse may be desired.

Various high molecular weight organic fluids, alone or in combination,may be used as the working fluid in system 20. These fluids includerefrigerants such as, for example, R125, R134a, R152a, R245fa, andR236fa. In other applications fluids other than high molecular weightorganic fluids may be used, e.g., water and ammonia.

System 22 also includes a power electronics package 86 connected togenerator 26. Package 86 converts the variable frequency output powerfrom generator 86 to a frequency and voltage suitable for connection tothe grid 87, e.g. 50 Hz and 400 V, 60 Hz and 480 V or other similarvalues.

Discussing generator 26 in more detail, in one embodiment the generatoris a direct-drive, permanent magnetic, generator. Such a construction isadvantageous because it avoids the need for a gearbox, which in turnresults in a smaller and lighter system 20. Various aspects of theinvention described herein may, of course, be effectively implementedusing a generator having a gearbox mechanically coupled between turbinerotor 104 of turbine 24 and generator rotor 74 of generator 26, and asuitable wound rotor that does not include permanent magnets, e.g., adoubly wound, induction-fed rotor. In addition, in certain applicationsdirect-drive synchronous generators may be used as generator 26. Therated power output of generator 26 will vary as a function of theintended application. In one embodiment, generator 26 has a rated poweroutput of 5 MW. In another embodiment, generator 26 has a rated poweroutput of 50 KW, and in yet other embodiments, generator 26 has a ratedpower output somewhere in between these values, e.g., 200 KW, 475 KW,600 KW, or 1 MW. Rated power outputs for generator 26 other than thoselisted in the examples above are encompassed by the present invention.

To permit high-speed (e.g., on the order of 20,000-25,000 rpm)operation, and to minimize maintenance, it may be desirable in someembodiments of generator 26 to support generator rotor 74 for rotationalmovement using magnetic radial bearings 88 (see FIG. 4 ). In oneembodiment, magnetic radial bearing 88 a is positioned adjacent an endof generator rotor 74 proximate turbine 24 and magnet radial bearing 88b is positioned adjacent an opposite end of the rotor. As discussed morebelow, this placement of bearings 88 enables in large part the overhungconstruction of turbine 24. Similarly, axial movement of generator rotor74 may be controlled through the use of magnetic axial thrust bearing89. Magnetic radial bearings 88 and magnetic axial thrust bearing 89 arecontrolled by a controller 90 that adjusts power delivered to thebearings as a function of changes in radial and axial position ofgenerator rotor 74, as detected by sensors (not shown) coupled to thecontroller, all as well known to those of ordinary skill in the art.

In another embodiment of the invention, fluid-film bearings may be usedin place of magnetic radial bearings 88 and thrust bearing 89. Forpurposes of illustration, the schematic depiction of magnetic bearings88 and 89 in FIG. 4 should be deemed to include, in the alternative,fluid-film bearings. As is known, fluid-film bearings support the totalrotor load on a thin film of fluid, i.e., gas or liquid.

Optionally, in addition to magnetic bearings 88 and 89, rolling elementradial bearings 92, e.g., radial bearings 92 a and 92 b, may be providedat opposite ends of rotor shaft 93 of generator rotor 74 surrounding therotor shaft, typically adjacent magnetic bearings 88 a and 88 b,respectively. Rolling element radial bearings 92 support generator rotor74 and its shaft 93 in substantially coaxial relation to rotational axis106 when magnetic bearings 88 and 89 are not energized. Moreparticularly, rolling element radial bearings 92 provide a rest pointfor generator rotor 74 when magnetic bearings 88 are not activated andprovide a safe landing for the generator rotor in the event of a suddenelectronic or power failure. It may be desirable in some cases to sizerolling element radial bearings 92 to support generator rotor 74 with arelatively loose fit so that during operation when magnetic bearings 88and 89 are energized, the rotor has limited, if any contact, withrolling element radial bearings 92, even during times of maximum radialdeflections of generator rotor 74 due to perturbations in the operationof magnetic bearings 88. When fluid-film bearings are used in place ofmagnetic radial bearings 88, rolling element radial bearings 92 aretypically not required, although in some applications it may bedesirable to include such radial bearings.

In one embodiment, rolling element radial bearings 92 are sized topermit rotor shaft 93 to deviate radially from perfect coaxial alignmentwith rotational axis 106 an amount that is 1.01 to 5 times as great asthe maximum radial deviation of shaft 93 from rotational axis 106 thatmay occur when magnetic radial bearings 88 are fully activated,including during times of major radial deflection that may occur due toperturbations of the magnetic radial bearings, e.g., from a fluiddynamic instability or a failed control system or a power failure(without backup). In another embodiment, this deviation permitted byradial bearings 92 is about 2 to 3 times as great as the radialdeviation of shaft 93 from rotational axis 106 that occurs when magneticbearings 88 are activated, again including during major perturbationsthat occur over time. Rolling element radial bearings 92 are oftenreferred to as “bumper bearings” or “backup bearings” in the art.

While beneficial for the reasons discussed above, rolling element radialbearings 92 also present a challenge because the radial clearance ofsuch bearings is much higher than the desired clearances for theconventional seals (not shown in detail) of turbine 24. Typical rollingelement radial bearings 92 have a radial clearance on the order of 0.005to 0.015 inch. By contrast, desired radial clearances for the seals ofturbine 24 are typically on the order of 0.000-0.001 inch. As generator26 is assembled, shipped and stored, or during a loss of levitation ofgenerator rotor 74 during operation due to failure of magnetic bearings88, the generator rotor will drop to rolling element radial bearings 92.A consequence of such “play” in generator rotor 74 is that portion ofshaft 93 proximate rolling element radial bearings 92, along with sealsin turbine 24, can be damaged over time. Indeed, in certainapplications, as few as 1-10 “bumper” events can cause sufficient damageto components of turbine-generator assembly 20 that disassembly andrepair/replacement of such components is required.

A solution to this problem is to add a radial brush seal 94 (FIG. 4 )adjacent one or more of magnetic bearings 88 and/or rolling elementradial bearings 92, or to substitute a brush seal for the rollingelement radial bearings (i.e., the bumper bearings). As used in suchcontext, brush seal 94 is designed to withstand substantial radialforces before deforming. Such deformation is temporary, with brush seal94 being constructed so that it springs back quickly to its priorconfiguration. In other words, brush seal 94 is self-healing. Thestiffness of each brush seal 94 is selected based upon the weight ofgenerator rotor 74 and turbine rotor 104 (discussed below) coupled withthe generator rotor, and the extent of radial movement of the rotors 74and 104 that is permissible given the overall design and operatingparameters, respectively, of generator 26 and turbine 24. In oneembodiment, the stiffness of brush seals 94 is selected so that theextent of radial deviation of generator rotor 74 from co-axial alignmentwith rotational axis 106 that occurs when the rotor is supported by justthe brush seals is 1 to 5 times greater than the extent of maximumradial deviation of generator rotor 74 from co-axial alignment withrotational axis 106 that occurs when magnetic bearings 88 are fullyactivated and supporting generator rotor 74 for rotational movementthrough the course of normal operation. In another embodiment, suchextent of radial deviation is 1.2 to 4 times greater than the extent ofradial deviation of generator rotor 74 from co-axial alignment withrotational axis 106 that occurs when magnetic bearings 88 are fullyactivated and supporting generator rotor 74 for rotational movementthrough the course of normal operation. In another implementation,generator rotor 74 is free to move a first radial distance out ofco-axial alignment with rotational axis 106 when magnetic bearings 88are not activated and the generator rotor does not move radially morethan a second radial distance out of co-axial alignment with rotationaxis when supported by brush seals 94. In this implementation, thesecond radial distance is no more than 0.8 times the first radialdistance, and in some implementations ranges from 0.2 to 0.6 times thefirst radial distance.

Referring now to FIGS. 2 and 4-10 , turbine 24 will be described in moredetail. In the embodiment illustrated in FIG. 4 a , turbine 24 is anoverhung axial turbine and includes a housing 98 having an axial inlet100 and a radial outlet 102. Turbine 24, in one embodiment, is amulti-stage turbine, with the embodiment shown in FIG. 4 a having threestages. In other embodiments discussed more below, turbine 24 may be asingle-stage overhung radial turbine as show in FIG. 4 b , and amulti-stage overhung radial turbine as shown in FIG. 4 c . Consistentwith this overhung configuration, no radial bearings are included inturbine 24, 324, 424 for radially supporting the rotor in the turbinefor rotational movement, As discussed above, turbine 24 is constructedso that the working fluid is expanded as it is transported through theturbine, with the result that the cold end of the turbine, i.e., the endproximate radial outlet 102, is positioned adjacent generator 26. Thisarrangement reduces heat transfer from turbine 24 to generator 26.

Turbine 24 includes a turbine rotor 104 that rotates about rotationalaxis 106 and a stator 108 that is fixed with respect to housing 98. Asdiscussed more below, in one example of turbine 24 featuring a modulardesign, turbine rotor 104 includes a plurality of individual bladedplates 110 and stator 108 includes a plurality of individual plates 112positioned in alternating, inter-digitated relationship with the rotorplates, as best seen in FIGS. 5, 6 and 9 . Rotor plates 110 and statorplates 112 are positioned within housing 98 in the cavity 114 formed atthe region between inlet 100 and outlet 102. As best illustrated inFIGS. 9 and 10 , radially innermost portions of stator plates 112 arespaced from portions of turbine rotor 104 positioned between rotorplates 110 so as to form a gap 115 sealed by seals 116 provided on suchradially innermost portion of the stator plates. In the portion ofturbine 24 illustrated in FIG. 5 , a plurality of stator spacer segments117, one corresponding to each rotor plate 110, is provided inalternating, inter-digitated relationship with radially outer portionsof stator plates 112. Each spacer segment 117 is positioned radiallyoutwardly of a corresponding respective rotor plate 110. In thealternative embodiments of turbine 24 illustrated in FIGS. 9 and 10 ,spacer segments 117 are formed as an integral portion of stator plates112 (spacer segments are not separately labeled in FIGS. 9 and 10 ). Inany event, in each of these embodiments, each spacer segment 117 issized with respect to its corresponding respective rotor plate 110 sothat a gap 118 is provided between a radially outermost portion of therotor plate and the radially innermost portion of the spacer segment.Seals 119 (see FIG. 9 ) may be provided in gap 118 in certainembodiments of turbine 24.

As best illustrated in FIGS. 9 and 10 , each rotor plate 110 includes afirst contact surface 130 and a second contact surface 132 that contactsthe first contact surface. Similarly, each stator plate 112 includes afirst contact surface 134 and a second contact surface 136 that contactsthe first contact surface. Contact surfaces 130, 132, 134 and 136 aresubstantially flat and substantially parallel. Further, they arearranged to be substantially perpendicular to rotational axis 106. Inone embodiment, contact surfaces 130, 132, 134 and 136 are flat in therange 0.00005″ to 0.020″, and in certain embodiments in the range0.0005″ to 0.005″, as measured with respect to a root mean squareversion of such surfaces. Further, in one embodiment contact surfaces130 and 132 of rotor plates 110, and contact surfaces 134 and 136 ofstator plates 112, deviate from perfectly parallel by an amount in therange 0.0001″ to 0.015″, and in certain embodiments in the range 0.0005″to 0.005″. Spacer segments 117, when provided, preferably have contactsurfaces that are similarly flat and parallel to contact surfaces 130,132, 134, and 136, as discussed above.

Referring now to FIGS. 7 and 8 , in certain implementations of turbine24, it may be desirable to circumferentially clock one rotor plate 110with respect to an adjacent rotor plate, e.g., clocking rotor plate 110a with respect to plate 110 b. Similarly, it may be desirable tocircumferentially clock one stator plate 112 with respect to an adjacentstator plate, e.g., clocking stator plate 112 a with respect to plate112 c. Desired performance specifications for turbine 24 will influencethe extent of clocking provided, as those skilled in the art willappreciate. When pairs of rotor plates 110 being clocked both have anequal number of vanes 140, in one embodiment a first rotor plate 110,e.g., plate 110 a, is clocked with respect to a second adjacent rotorplate, e.g., plate 110 b, zero to one vane pitch, i.e., (0)S to (1)S.Similarly, when pairs of stator plates 112 being clocked both have anequal number of vanes 142, in one embodiment a first stator plate 112,e.g., plate 112 a is clocked with respect to an adjacent stator plate,e.g., plate 112 c, zero to one vane pitch, i.e., (0)S to (1)S. Whenpairs of rotor plates 110 being clocked both have an unequal number ofvanes 140, in one embodiment a first rotor plate 110, e.g., plate 110 a,is clocked with respect to a second adjacent rotor plate, e.g., plate110 b, somewhere in the range of 0 to 360 degrees. Similarly, when pairsof stator plates 112 being clocked both have an unequal number of vanes142, in one embodiment a first stator plate 112, e.g., plate 112 a isclocked with respect to an adjacent stator plate, e.g., plate 112 c,somewhere in the range of 0 to 360 degrees. Known turbine flowanalytical and experimental methods are used to guide selection of theoptimal amount of clocking in this range of 0 to 360 degrees.

With continuing reference to FIGS. 7 and 8 , in one embodiment adjacentstator plates 112 are clocked with respect to one another using analignment system featuring a plurality of circumferentially spaced bores160 positioned along a peripheral section 162 of a stator plate 112,e.g., stator 112 c, only five of which are illustrated in FIG. 7 forconvenience of illustration. In one implementation, adjacent bores 160are circumferentially spaced one vane pitch S. The alignment system alsoincludes a bore 164 in a peripheral section 166 of spacer segments 117.Further, a blind bore 168 may be provided in a peripheral section 170 ofa stator plate 112, e.g., stator plate 112 a, immediately adjacent thestator plate, e.g., stator plate 112 c, in which bores 160 are provided(rotor plate 110 b and spacer plate 117 are intervening, of course). Inone embodiment, bores 160, 164 and 168 are spaced a substantiallyidentical radial distance from rotational axis 106, and have asubstantially identical diameter. The alignment system further includespin 172, which is sized for receipt, typically using a mild frictionfit, in a selected one of bores 160 and in bore 164. When so positioned,pin 172 locks stator plate 112 c in selected circumferential alignmentwith adjacent spacer segment 117. The selected circumferential clockingbetween adjacent stator plates, e.g., plates 112 a and 112 c, isachieved by next locking spacer section 117 to stator plate 112 a usingpin 174 inserted in bores 164 and 168. A similar system for clockingadjacent rotor plates 110 may also be employed, as discussed more belowin connection with FIGS. 9 and 10 . As discussed above, selection of oneof the plurality of bores 160 that receives pin 172 is determined basedon the extent of circumferential clocking desired between adjacentstator plates 112. The present invention encompasses other approaches tocircumferentially clocking adjacent rotor plates 110 and stator plates112, as those skilled in the art will appreciate.

With particular reference to FIG. 9 , rotor plates 110 and stator plates112 are, in one implementation, spaced so that axial distance 178between vanes 140 of a rotor plate 110 and vanes 142 of an adjacentstator plate 112 is in the range of two axial chords to ¼ of 1% of anaxial chord, and in certain embodiments ⅓ to 1 chord, as measured withrespect to the chord of the immediately upstream one of the rotor orstator plates. For example, vanes 140 of rotor plate 110 identified asR3 in FIG. 9 are axially spaced distance 178 a from immediately adjacentvanes 142 of stator plate 112 identified as S3 a chord distance C_(x),S3 that is in the range of two axial chords to ¼ of 1% of an axialchord, and in certain embodiments is spaced ⅓ to 1 chord. Additionally,the stage reaction for turbine 24 may be of any conventional level.When, however, axial thrust levels must be controlled to meet availablethrust capability of generator 26, then very low stage reaction may bedesirable, with common values in one example ranging from −0.1 to 0.3and often falling in the range of −0.05 to +0.15. When very low stagereaction cannot be achieved, for example with multi-stage radial inflowturbine 424 illustrated in FIG. 4 c , then the second stage may bereversed so that the two radial turbines work back-to-back, leaving thelast stage discharge still facing the generator.

Referring to FIGS. 4-6, 9 and 10 , in connection with the assembly ofthis embodiment, rotor plates 110 and stator plates 112 are positionedin alternating, inter-digitated relationship. In one embodiment, rotorplates 110 include a plurality of bores 186 (see FIG. 5 ) in radiallyinner portions of the plates, which bores are sized to receive afastener, such as bolt stud 188, which extends through the plates and issecured to stub shaft 189 via threaded bores 190 in the stub shaft.Generator rotor shaft 93 may include a threaded male end 192 that isreceived in a threaded bore 194 in stub shaft 189.

Stator plates 112, and spacer segments 117 if provided, may, forexample, be secured together in alternating, inter-digitatedrelationship so as to form a unitary cartridge 198. The latter may bereleasably secured in cavity 114 (FIG. 6 ) of housing 98 using knownfasteners and other devices. In one embodiment, cartridge 198 may besecured in cavity 114 by lock ring 200, which is engaged with a snap fitin a correspondingly sized recess 201 in in the cavity. With thisconstruction, when lock ring 200 is installed, stator plates 112, andsegments 117 when provided, are driven against shoulder 202 formed incavity 114 in housing 98, thereby holding the plates and segmentssecurely in place. In certain embodiments of turbine 24, rotor plates110 may be secured together with pins 203 (see FIGS. 9 and 10 ) receivedin bores 204 (see FIGS. 8, 9 and 10 ) to ensure no relative rotationalmovement occurs between rotor plates. Similarly, in other embodiments ofturbine 24, stator plates 112 and spacers 117 may be secured togetherwith pins 172 (see FIGS. 9 and 10 ), as discussed above, to ensure norelative rotational movement occurs. Pins 172 may also penetrate intofloor 204 of housing 98 (such penetration not being shown) from thedownstream-most spacer 117 or stator plate 112, if desired to assure norelative motion. A nose cone 206 may be provided, with one embodimentbeing threadedly engaged with threaded bore 208 in the furthest upstreamstator plate 112 (identified in FIGS. 9 and 10 as S1). Alternatively,machine screws may be used to fasten nose cone 206 to first stator plate112. With reference to FIGS. 5, 6, 9 and 10 , in some implementations itmay be desirable to rotationally align and secure together rotor plates110, stator plates 112, and if provided, spacers 117, using one or morepins 210 and/or one or more bolt studs 212 that extend through the rotorplates, stator plates and spacers. Pins 210 may be used for precisionrotational alignment of rotor plates 110, stator plates 112 and spacers117, and if received in these components with a sufficient force fit,may also hold these components together to form a unitary structure,namely unitary cartridge 198. Bolt studs 212, in addition to providingsome measure of rotational alignment, also draw together the rotorplates, stator plates and spacers to form a unitary structure, namelyunitary cartridge 198.

By providing separate rotor plates 110 and stator plates 112, and bymaking such plates relatively flat as discussed above, these plates maybe assembled as a cartridge 198 (see FIG. 5 ) that may be positioned inand removed from cavity 114 in housing 98 as a unitary assembly. Asdiscussed more below, the provision of cartridge 198 permits a universalturbine 24 to be readily adapted for its intended application andinterchanged for maintenance or new loading requirements.

In some applications, it will be desirable to more substantially isolategenerator 26 from turbine 24. To achieve this objective, as bestillustrated in FIG. 6 , it may be desirable to include a seal 220surrounding stub shaft 189 of turbine 24 proximate the radiallyinnermost portion of backplate 250. Seal 220 may be implemented as alabyrinth seal, a brush seal, a close-tolerance ring seal or using otherseals known in the art.

The embodiment of turbine 24 shown in FIGS. 4-6 , is designed to permitready manufacture of versions of the turbine having differently sizedrotors 104 and stators 108. By providing a single housing 98 for turbine24 while permitting construction of turbines with varying operatingparameters using that single housing, the turbine can be manufactured ona cost-efficient basis to the specifications of a given application.This flexible design is achieved in part by designing and sizing housing98 of turbine 24 so that the largest-diameter turbine rotor 104contemplated for the turbine may be received within cavity 114 andthrough the use of the cartridge design discussed above. In particular,after the desired operating parameters of turbine 24 are determined forthe application in which the turbine will be used, then the number andsize of plates 110 used in turbine rotor 104, and plates 112 and spacersegments 117 used in stator 108, are determined.

Consistent with the objective of providing a turbine 24 that can bereadily modified to meeting desired operating parameters, housing 98 isdesigned to facilitate such modification. One aspect of such design ofhousing 98 involves providing floor 204 with a thickness sufficient toaccommodate turbine rotor 104 and stator 106 having varying radialheights. Δr, as measured between said rotational axis and an outermostportion of said at least one turbine rotor, said axial turbine includinga hood having a floor with a first thickness, wherein said firstthickness is selected to permit said floor to be machined on the insideto a thickness sufficient to accommodate said at least one turbine rotorwith a radial dimension that varies between Δr and 1.4Δr. Further,housing 98 is provided with a configuration that permits easy access tofloor 204 by conventional machine tools, e.g., a 5-axis CNC millingmachine or a CNC lathe, that can be used to machine the floor so as tocreate a cavity 114 sized to receive turbine rotor 104 and stator 106with the desired radial heights.

Another aspect of providing a modifiable housing 98 is to include abackplate 250 having a thickness that may be adjusted so as toselectively vary width l4, i.e., the distance l4 between backplate 250and housing wall 252, and to selectively vary width l1, i.e., the exitwidth. In this regard, width l4 may be varied so that it ranges from onehalf to four times the width of diffuser exit l1. Backplate 250 may bean integral portion of housing 98 in some embodiments and a separateelement in others, as illustrated in FIG. 4 . Backplate 250 preferablyincludes one or more ports 254 through which vapor in gap 70 may beexhausted and delivered to the exhaust flow path of turbine 24 andultimately via fluid connection 34 to condenser 36. If desired, flowsplitter 256 may be provided immediately downstream of turbine rotor 104and stator 106 as another way to tailor the performance of turbine 24.As another optional feature, an extension plate 258 may be added to nose260 of floor 204 of housing 98, as best seen in FIG. 6 .

Housing performance depends on several factors, but alignment of theentry flow at the housing inlet 100 and housing base dimensions areimportant as taught in the literature. A very good flow entry providesfor diffuser exhaust flowing up the housing backplate 250, as configuredin FIG. 4 . An essential design variable is to set L4=l4/l1 to a valueof 0.5 to 4, often in the range of 2 to 3, in order to have highperformance (maintaining good diffuser Cp). This means that the diffuserexit width (l1) and the hood floor width (l4) must be controlled. Theexit width l1 also controls the performance of the diffuser as itcontrols the diffuser overall area ratio, which is a first order designparameter; hence a conflict can arise. If l1 is increased for thediffuser, it will hurt the housing. This is controlled by starting witha generous housing design to cover a wide range of power levels (up to 5MW for certain designs) and then adjusting operating parameters bymodifying backplate 250 and the nose 260 of floor 204. Another designvariable is to introduce diffuser splitter 256 (FIG. 6 ), which givesindependent control on l1, thereby permitting a selected change in thediffuser exit value. Further performance tailoring can be achieved byselection of an extension plate 258 (FIG. 6 ) of suitable height andthickness.

Turbine 24 is depicted in FIG. 4 a as a multi-stage axial turbine 24,but turbine-generator system 20 is not so limited. In this regard, andwith reference to FIG. 4 b , in an alternative embodiment,turbine-generator system 20 may include a radial turbine 324 having asingle stage. Like numbers are used in FIG. 4 a and FIG. 4 b to identifylike elements, and for brevity, a description of like elements isomitted in connection with the following description of radial turbine324. The latter includes a single rotor 104 and a single stator 108.Like the axial turbine 24 depicted in FIG. 4 a , radial turbine 324 maybe implemented as a unitary cartridge 198 that may be releasably securedto generator shaft 93 with a bolt stud 188. Turbine 324 may include aninlet flange ring 333, and an outer flow guide 334 attached to housing98 with known fasteners. Nose cone 206 and stator 108 may be releasablesecured to housing 98 with a known fastener, such as bolts 337.

Turning next to FIG. 4 c , in an alternate embodiment, turbine-generatorsystem 20 may include a multi-stage radial turbine 424. Like numbers areused in FIG. 4 a and FIG. 4 b to identify like elements, and forbrevity, a description of like elements is omitted in connection withthe following description of radial turbine 424. The latter includes tworotors 104 and two stators 108. Radial turbine 424 may be implemented asa unitary cartridge 198 that may be releasably secured to generatorshaft 93 with a bolt stud 188. Turbine 424 may include an inlet flangering 333, and an outer flow guide 334 attached to housing 98 with knownfasteners. Nose cone 206 and stators 108, together with intermediateflow guide 441 positioned between the stators, may be releasable securedto housing 98 with a known fastener, such as bolts 337. The two stators108 of turbine 424 and intermediate flow guide 441 may be securedtogether with bolts 339 or other known fasteners so as to create unitarycartridge 198. Intermediate flow guide 441 is functionally analogous tostator spacers 117 in the version of turbine 24 illustrated in FIGS. 5and 6 .

Depending on the desired balancing of thrust in turbine-generator system20, it may be desirable to configure rotors 104 of a multi-stage radialturbine in a back-to-back arrangement, as illustrated in FIG. 4 d withrespect to radial turbine 524. In this regard, rotor 104 a is positionedso it backs up to rotor 104 b, with the rotors being coupled to rotatetogether. Stator 108 is positioned between rotors 104 a/104 b, andincludes bearings 526 for rotatably supporting a portion of rotor 104 bthat extends through the stator. Turbine 524 further includes a frontface plate 550 through which gas transfer tubes 552 extend, with the gastransfer tubes terminating at interior plenum 554. Gas flow enteringturbine 524 flows into tubes 552, is delivered to interior plenum 554,exits the plenum causing rotor 104 a to rotate, flows over stator 108,then drives rotor 104 b and finally exits the turbine.

Although not specifically illustrated, turbine-generator system 20 mayalso be implemented using a mixed-flow turbine. The latter is verysimilar in design to radial turbine generators 324 and 424, and so isnot separately illustrated.

By placing rotor 104 in a reverse orientation so that the low-pressure,cooled working fluid is discharged from the last rotor stage of turbine24 proximate generator 26, heat transfer to the generator is minimized,thereby prolonging generator life. The low-pressure exhaust of turbine24, as a consequence of its reverse orientation, draws the second volumeof working fluid out of gap 70 in generator 26 via ports 254 and intothe discharge stream of turbine 24 while balancing thrust forcessufficiently so that the generator thrust bearing 89 can handle theremaining axial load of turbine 24. Such a design is efficient, compactand thermally efficient.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

What is claimed is:
 1. A turbine housing, comprising: an exhaust hoodhaving a floor and a sidewall; wherein a first side of the floor and thesidewall define an exit plenum and a second opposite side of the floorpartially defines a cavity configured to receive at least one rotor andat least one stator; wherein the floor has an oversized thickness thatis designed and configured to be machined to define a dimension of thecavity sufficient to receive the at least one rotor and at least onestator for a range of turbine power output ratings; wherein the housingis designed and configured to accommodate a unitary cartridge that isremovably positioned in the cavity, the unitary cartridge including theat least one rotor and the at least one stator, wherein the oversizedthickness is sized to be machined to accommodate a range ofdifferently-sized unitary cartridges.
 2. The turbine housing of claim 1,further comprising a backplate removably coupled to the housing, thebackplate and floor defining a diffuser passage located between thecavity and the exit plenum, wherein the backplate is configured to beremoved to facilitate the machining of the floor.
 3. The turbine housingof claim 1, wherein the cavity is configured to receive the at least onerotor removably coupled to a shaft in an overhung configuration and theat least one stator removably coupled to a wall of the cavity.
 4. Theturbine housing of claim 1, wherein the oversized thickness of the flooris configured to provide a range of cavity sizes sufficient to accept asize of the at least one rotor having a radial height in the range of H1to 1.4*H1.
 5. The turbine housing of claim 1, further comprising abackplate, wherein the floor and a first portion of the backplate definea diffuser passage located between the cavity and the exit plenum andwherein a second portion of the backplate extends laterally from an exitof the diffuser passage and partially defines the exit plenum, wherein athickness of the second portion is oversized and configured to bemachined to define a dimension of the exit plenum according to a designparameter of the turbine and/or a size of the diffuser passage.
 6. Theturbine housing of claim 1, further comprising a backplate thatpartially defines a diffuser passage, wherein a thickness of thebackplate is oversized and configured to be machined to define adimension of the diffuser passage according to a design parameter of theturbine and/or a size of the exit plenum.
 7. A method of manufacturing aturbine, comprising: obtaining a universal housing that includes anexhaust hood, wherein a first side of a floor of the exhaust hoodpartially defines an exit plenum and a second opposing side of the floorpartially defines a housing cavity, the cavity designed and configuredto accommodate at least one rotor, wherein the floor has an oversizedthickness that is configurable for a range of sizes of the at least onerotor corresponding to a range of turbine power output ratings;determining a turbine power output rating; obtaining at least one rotorhaving a size corresponding to the determined power output rating;machining material away from the floor to increase a size of the cavitya sufficient amount to accommodate the obtained at least one rotor; andinstalling the at least one rotor in the cavity.
 8. The method of claim7, wherein the machining further includes machining material away fromthe floor to increase a size of the cavity a sufficient amount toaccommodate at least one stator, further wherein the installing includessecuring the at least one stator to the housing and coupling the atleast one rotor to a shaft for rotational movement in the cavity.
 9. Themethod of claim 7, wherein the turbine power output rating is sufficientto drive an electric generator that produces a maximum electric poweroutput at a target value in the range of 50 KW to 5 MW.
 10. The methodof claim 7, where the thickness of the floor is sized to be machined toaccommodate a radial height of the at least one rotor in the range of H1to 1.4*H1.
 11. The method of claim 7, wherein the housing is designedand configured to accommodate a unitary cartridge that is removablypositioned in the cavity, the unitary cartridge including the at leastone rotor and at least one stator, wherein the machining includesmachining the floor to decrease a thickness of the floor a sufficientamount to receive the unitary cartridge in the cavity.
 12. The method ofclaim 7, wherein the housing further includes a removable backplate,wherein a first portion of the backplate and the floor define a diffuserpassage having an exit and having a width L1 and a second portion of thebackplate defines a first portion of the exit plenum adjacent thediffuser passage exit having a width L4, the method further includingthe step of machining the backplate so the width L4 ranges from one halfto four times the width L1.
 13. A method of manufacturing a plurality ofturbines wherein each turbine in said plurality of turbines ismanufactured starting with one of a plurality of substantially identicalturbine hoods, each turbine hood having a cavity for receiving a rotorstage and a floor with a first thickness, wherein the floor defines aportion of the cavity and the cavity has an inside diameter D1, themethod comprising; machining material away from the floor of a first oneof said plurality of turbine hoods to increase the inside diameter D1 ofthe cavity to an inside diameter D2, where D2 is selected to permit thecavity to accommodate a first rotor stage having a radial height H1, thefirst rotor stage being designed and sized to be positionable in thecavity of the first one of the plurality of universal turbine hoods; andmachining material away from the floor of a second one of said pluralityof turbine hoods to increase the inside diameter D1 of the cavity to aninside diameter D3, wherein D3 is different than D2 and is selected topermit the cavity to accommodate a second rotor stage having a radialheight H2 that is different than radial height H1, the second rotorstage designed and sized to be positionable in the cavity of the secondone of the plurality of turbine hoods.
 14. The method of claim 13,wherein said machining is performed in accordance with a turbine designdeveloped to produce a turbine having a power output sufficient to drivean electric generator that produces a maximum electric power output at atarget value in the range 50 KW to 5 MW.
 15. The method of claim 13,wherein at least one of the plurality of universal turbine hoodsincludes a removable backplate, further wherein the machining of thefloor of the at least one of the plurality of turbine hoods is performedwith the backplate removed.
 16. The method of claim 13, wherein thefirst thickness is sufficient to accommodate a size of the rotor stageranging from the radial height H1 to 1.4*H1.
 17. The method of claim 13,wherein the plurality of turbine hoods are designed and configured toaccommodate a range of sizes of unitary cartridges removably positionedin the cavity, the unitary cartridges each including the rotor stage anda stator, wherein D2 is selected for the installation of a first unitarycartridge having a first size and D3 is selected for the installation ofa second unitary cartridge having a second size that is different thanthe first size.
 18. The method of claim 13, wherein at least one of theplurality of turbine hoods includes a backplate, the floor and backplatedefining a diffuser passage located downstream of the cavity, thediffuser passage having a width L1, the at least one of the plurality ofturbine hoods further including a hood wall, the backplate and hood walldefining an exit plenum located downstream of the diffuser passage, thehood wall axially spaced a distance L4 from the backplate, wherein themethod further includes machining the backplate so the distance L4ranges from one half to four times the width L1.